Dynamics of weedy rice soil seedbank under different control strategies in Italian rice fields: survey and model study

Abstract

The abundance of weedy rice (Oryza sativa L.) in the soil seedbank was estimated in 2011 in Italian rice (Oryza sativa L.) fields with different histories of IMI-resistant Clearfield® rice varieties (CL), non-Clearfield® varieties (NCL) and planting methods. A model was used to predict weedy rice seedbank dynamics over time under different control strategies. Soil samples were taken from 50 rice fields cultivated with CL varieties consecutively for 0, 1, 2, or 3 years and weedy rice seedbank data were used in a model considering eight scenarios: A) rice monoculture with CL and NCL varieties in alternate years; B) two years of CL, followed by one year with NCL; C) three years of CL followed by one year of NCL; D) rice monoculture with only CL; E) rice monoculture with only NCL; F) two years of CL followed by one year of rotation with another crop (CR), and then by an additional year with NCL; G) one year of CR followed by two years of CL, and then by one year of NCL; H) two years of CR followed by two years of CL. Weedy rice seedbank exceeded 1,000 seeds m−2 in the surveyed fields with no significant differences between rice planting methods. Highest densities were found in fields cultivated for one year with CL varieties. Simulations indicated that where CL varieties were used in rice monoculture susceptible weedy rice seedbank reduced gradually, allowing a depletion after 17, 13, 11, and 9 years in scenarios A), B), C), and D), respectively. The weedy rice seedbank increased in NCL monoculture (E) and declined significantly in crop rotation scenarios (F, G, H). The simulations indicated that the introduction of crop rotation is crucial for obtaining a relatively fast reduction of weedy rice seedbank and delaying the evolution of herbicide-resistant populations.

Insights into the genetic spatial structure of Nicaraguan weedy rice and control of its seed spread

“…Employing the grain appearance index established in this study, combined with general scanner and image analysis software (such as SmartGrain 16 ) will improve the efficiency and reliability of seed purity inspections. Other preventive methods include pre‐emergence herbicide applications, water management, adoption of laser‐guided land leveling technology and crop rotation 42–44 …”

“…Other preventive methods include pre-emergence herbicide applications, water management, adoption of laser-guided land leveling technology and crop rotation. [42][43][44] To break the life cycle of WR in the soil seedbank, WR plants and their panicles should be removed from fields after the heading stage and before the dough stage. In addition, although planting herbicide-tolerant varieties along with the use of chemical control is convenient and effective, 45 our study documented outcrossing events randomly occurring in each district, indicating that there is pollen-mediated gene flow between WR and cultivated rice.…”